Just wondering if anyone can help me. My fuel gauge was working to a point, only going to half full even when I filled the tank. I pulled the sending unit and found there was a lot of build up on the center rod and the float would not go past it. I cleaned it and put it back in. When I checked my gauge it was where it should be almost empty as I am getting ready to pull the fuel tank and clean it.
I pulled the IP to see if I could clean and rebuild the rheostat as I had no dash lights. I got everything out and cleaned the rheostat, put it back together and reinstalled the IP. While I was putting the IP back together I noticed that my fuel gauge was way below "R" but was hoping that when I hooked everything back up the power to it would cause it to jump back to where it should be. It didn't.
I still haven't put fuel in it as I ran out of time and haven't yet pulled the tank but hope to have that done in the next couple days. I also developed a leak at the primer pump so I am waiting for the new "no leak" primer to come in before I do this.
Any ideas what I need to do to get my fuel gauge back to where it should be? Did I do something to ruin it while I was cleaning the rheostat?

PS: After cleaning the rheostat and reinstalling it, I now have dash lights. Thanks to this site and teaching me what was wrong and what I needed to do to fix it.

Car is a 85 300DT W123 body style

I replaced my erratic sending unit, at the time new ran $65, new gasket also.

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83 SD

84 CD

Okay, then in the process it went from "almost empty" to way below "R"??

Did the reserve light come on? Typically MB fuel guages are tricky critters that drop like stones in last quarter. Often varying with tank nearly empty. Seen em suddenly read extra gallons just from climbing a hill or parking on incline.

Difference between almost E and R is meaningless. Gotta throw at least 5 gals fuel in tank to see how guage behaves.

If dropped way below R after I took the IP out to rebuild the rheostat. Before that, the fuel gauge worked for the most part it just wouldn't go past 1/2 tank.
The warning light is on right now but the needle points almost at 9 o'clock right now. Now where close to the R.
I think I will pull the sending unit out again and rehook the wires and turn it upside down to see if the gauge goes more towards 12 o'clock. If so, is it possible that when I had the IP tore apart I moved the needle and that just needs to be moved back clockwise?

Just make sure the float on the tank indicator can up and down easily. I used a rotozip sanding stone on mine, to get inbetween the tiny metal wires the float runs on. Got rid of all the rust.

Jeff 1991 300d

Well, I figure that while I had the IP out I must have moved the needle somehow. I pulled the sending unit out tonight and plugged it back in. I turned the key on and had my son turn it upside down so the float would move to the full position. The gauge moved clockwise and stopped right before it got to the R. Had him turn it to the proper position and it moved back counter clockwise.
"Lucky" for me the front of my IP needs to be glued back on so I was able to pull that and get to the needle. I saw somewhere on this site that you can use a fork to pull the needles off by slipping the fork behind them and prying them off. It came off and I reset it to point at the R. After that was done I flipped the sending unit again and it went straight to the full mark and then back to the correct position and it went straight back to the R.
I guess I learned that if I need to pull the IP apart again, I need to be more carefull when I set them down.